Such a laser device as described above is employed as a light source of a laser system such as a microscopes, profile measurement device, exposure device, inspection device, etc. The wavelength of output lights from laser devices are designed according to the usage and the functions of the laser system mounting such laser devices. Specifically, a combination of the wavelength of the fundamental wave laser light output from the laser light output unit and the kinds of wavelength conversion optical elements provided to the wavelength conversion unit is appropriately designed according to the usage and the functions of the aforementioned laser system (see Patent document #1).
In order to perform wavelength conversion by means of such a wavelength conversion optical element (non-linear optical crystal), there is a need to satisfy a phase matching condition in a wavelength conversion step. For example, in a case in which the phase matching is in critical phase matching (CPM), the angle of the wavelength conversion optical element is adjusted with respect to the laser light such that the incident angle of the laser light with respect to the optical axis of the wavelength conversion optical element matches a predetermined phase matching angle in a predetermined temperature environment. In a case in which the phase matching is in non-critical phase matching (NCPM), the temperature of the wavelength conversion optical element is adjusted such that the temperature of the non-linear optical crystal that forms the wavelength conversion element is maintained at a predetermined phase matching temperature in a predetermined laser light incident environment (in a state in which the incident angle of the laser light with respect to the optical axis of the wavelength conversion optical element is maintained at 90 degrees or otherwise 0 degrees) (see Patent documents #2 and #3).